The United States' Brian Harman and Brooks Koepka, and England's Paul Casey and Tommy Fleetwood shared the lead at the 117th US Open golf championship at the close of the second round at Erin Hills on Friday.

The four leaders, Harman (two-under 70), Koepka (70), Casey (71) and Fleetwood (70) ended the day on a total of seven-under 137, although the narrow field at the end of the second day promises an unpredictable weekend.

Dustin Johnson of the US, Rory McIlroy of Northern Ireland and Australia's Jason Day, the top-ranked golfers in the world, all missed the halfway cut set at one-over 145. They finished at four, five and 10 over par respectively.

It is the first time since the Official World Golf Rankings began in 1986 that the top three players have missed the cut at a major.

Three others in the top 10, No.6 Henrik Stenson, No.8 Alex Noren and No.10 Jon Rahm also missed the cut.

The player who stunned everyone was joint-leader Casey, who got a triple-bogey on the par-five 14th hole, and roared back into contention with five consecutive birdies. "It was a bit of a roller coaster," said Casey.

"Not every day you enjoy a round of golf with an 8 on the card, but I'm a pretty happy man," Casey told the tournament's website. "For me, it felt like (the course) played tougher today."